1. Field of the Invention
The present invention relates to cementitious products such as concrete, mortar, grout, and the like, and concrete products such as paving, paving blocks, concrete pipe, concrete blocks, cellular We concrete, extruded concrete and concrete statuary; and more particularly to an improved cementitious composition and process for producing cemetitious products having improved resistance to water penetration and other deleterious elements and agents.
2. Description of Related Art
Concrete is a widely used engineering construction material, generally comprising a cementing or bonding substance, usually cement, and most commonly portland cement; aggregate, such as gravel, stone and/or sand; and water. Other cementitious products, such as mortar or grout are made by varying the type of aggregate employed. The cementing substance, particularly hydraulic cement, usually reacts chemically with water to form a hard, stonelike mass, which during concurrent mixing with aggregate, forms concrete, mortar and other cementitious products.
While cementitious products, such as concrete, particularly as used for pavement, bridges, walls, dams and the like, are relatively durable, they deteriorate over time, often due to the penetration of water into the product, particularly due to the porous nature of the product. Excess water is always used in a concrete mix in order to facilitate pouring and placement of the concrete. If the exact amount of water needed to hydrate the cement is used, the concrete would not be pourable or placeable. The excess water found in the mix is non-compressible and substantially evaporates from the concrete as it cures, and the resultant mass becomes porous as evaporation progresses. The porosity further diminishes the durability of the concrete, providing locations for water to penetrate the concrete. In climates where freezing temperatures periodically occur, the water in the product tends to freeze during such periods, and when frozen expands, often causing cracks, spalling and accelerated disintegration of the product. The deterioration is particularly noticeable where metal is used for reinforcement of the concrete products, for example, in the form of reinforcing mesh or rods, for example xe2x80x9crebarsxe2x80x9d in concrete pavement and the like. Over time, water penetrates through the concrete which corrodes metal reinforcement, often causing visible stains on the surface of the product, as well as weakening of the structure of the product.
In prior attempts to reduce water penetration, detergents have been mixed into the mixture of water, cementing substance and aggregate, but the result has been only marginally decreasing the porosity of the resulting product. Other known additives such as pozzolanic materials and metal salts of fatty acids provide only marginal improvement in water resistance, and also decrease the strength of the product during curing.
Quality concrete has surfactants added to the mix. Surfactants decrease the need for excess water, while making the concrete mix pourable as if the added amount of excess water was present. The pourability of the concrete mix is referred to as xe2x80x9cslumpxe2x80x9d. These surfactants are known as water-reducers, plasticizers and in some cases xe2x80x9csuper-plasticizersxe2x80x9d. When surfactants are introduced into the concrete, the result is a less porous and somewhat stronger product. The strength increase is attributed to lower water/cement ratio and decrease in porosity. While surfactants improve the resistance to water penetration, surfactants alone provide too little improvement to be considered a solution to the problem.
Another proposal to reduce water penetration has been the introduction into the composition of a glycol ester of a C8-C22 22 fatty acid, such as the polyethyleneglycol ester of stearic acid, as in U.S. Pat. No. 4,878,948. The resulting product provides only incremental improvement in water penetration.
Other attempts at reducing water penetration of cementitious products have utilized surface treatments, using such treatments as aqueous dispersions of film forming synthetic polymers and coagulants, film forming water-based, wax-free emulsions of a C4 linear polymer composition used for both wood and concrete surfaces, and paraffin wax in solvent coatings. These surface treatments are impractical with large surfaces, such as pavements, and are ineffective over a period of time due to wear and erosion of the coating due to climatic elements and ultraviolet deterioration.
Therefore, there is a need for compositions and a process for substantially improving the water resistance of cementitious products, which compositions and process do not decrease the strength and other properties of the products.
There is a further need for improving the early strength of cementitious products, i.e., cement aggregate products. It is known that cement aggregate products, particularly such cement aggregate products as blocks, concrete masonry units and concrete pavers, achieve acceptable strength to permit their being shipped and used only after a relatively long period, usually a number of days. Such cement aggregate products, as blocks concrete masonry units and concrete pavers, are produced by pouring a mix of cement, aggregate and water into a mold. The least amount of water is utilized to permit the mix to be placed in the mold, so that the product will retain its shape upon removal after few seconds in the mold. The molded product is then placed on curing racks and allowed to remain on the racks, often while being heated, for a relatively lengthy period, until sufficient strength, usually approximately 1000 psi for concrete masonry units is attained so the products can be shipped and used.
Attempts have been made to increase the early strength of cement aggregate products, particularly concrete blocks, concrete masonry units, and the like, by adding an accelerator, such as calcium chloride triethanolamine or sodium silicate, to the mix or subjecting the product to steam or using type III cement. However, the addition of these accelerators, or the use of steam, increases the cost of producing the product and often its production time.
Thus, increasing the early strength of the product is advantageous in reducing the time and cost required for producing a shippable and usable product.
It is also known that cementitious products exposed to the elements and/or in moist conditions are subject to the growth of mildew and mold on their surfaces, detracting from their appearance and eventually to their discoloration and deterioration. Therefore, there is a need for cement aggregate products having improved resistance to the growth of mildew and mold in addition to improving the resistance of the products to the penetration and absorption of water.
Therefore, it is one object of the present invention to provide a composition which substantially improves the resistance of cementitious products to the penetration of water.
It is another object of the present invention to provide a process for the production of cementitious products which have improved resistance to the penetration of water.
It is still another object of the present invention to provide compositions and a process to reduce the amount of water required in the production of cementitious products which have improved resistance to the penetration of water.
Still another object of the present invention is to provide compositions and a process for improving the resistance against mildew and mold on the surface of cementitious products.
An object of this invention is to provide compositions and a process for improving the early strength of cement aggregate products.
Another object of this invention is to provide compositions and a process for improving the flowability of cementitious compositions.
Still another object of the invention is to provide compositions and a process for improving the resistance of cementitious products to the growth of algae on their surface.
Another object of the invention is to provide compositions and he a process for improving the resistance of cementitious products containing certain additives to deterioration from ultraviolet radiation of those additives within the products.
Still another object of the invention is to provide compositions and a process for improving the durability of cementitious products against deterioration as a result of cyclical freezing and thawing.
Another object of the present invention is to provide compositions and a process for providing cementitious products having lower weight per volume than cementitious products of the prior art.
It is still another object of this invention to provide compositions and a process which efficiently provide a vehicle for instituting property enhancing agents into cementitious products while improving the resistance of the cementitious products to the penetration and/or absorption of water into the products.
These and other objects and advantages of the present invention will be apparent from the following description.
In accordance with the present invention a process is provided for improving the resistance of a cementitious product to the penetration of water into the product in which a minor amount of an aqueous emulsion of a waxy substance or of rosin is combined with a major amount of water to form a substantially aqueous mixture which is utilized as the aqueous ingredient in the preparation of the cementitious product. For convenience, both rosin and waxy substances useful in the present invention are referred to as xe2x80x9cwaxy substancexe2x80x9d, and emulsions of both a waxy substance or of rosin are referred to herein as xe2x80x9cemulsion of a waxy substancexe2x80x9d, unless otherwise described. The composition of the present invention comprises an aqueous mixture including an aqueous emulsion of a waxy substance in an amount sufficient to improve the resistance to the penetration of water in a cementitious product admixed with cement and aggregate.
It is surprising and unexpected that the use of an aqueous emulsion of a waxy substance in the composition of water, cement and aggregate to form the cementitious product provides improved resistance to the penetration of water while substantially maintaining the strength of the product, particularly the early strength of the product, because it has generally been found that previous attempts to introduce wax and wax-like substances into the composition tended to weaken the resulting cementitious product. For example, the introduction of a wax in a solvent into the composition of water, cement, and aggregate used to produce a concrete product caused the resulting concrete product to have substantially less strength than the concrete product produced from a substantially identical composition without the wax. It is believed that the wax coated the aggregate particles and inhibited the adherence of the cement paste to the aggregate particles causing the weakening of the product as measured by testing the compressive strength of the product.
The aqueous emulsion in accordance with the present invention, in addition to an aqueous emulsion of rosin, can be an aqueous emulsion of wax of animal or vegetable origin, or of petroleum origin or similar substances. Waxes suitable for use in the aqueous emulsion of the present invention include: bees wax, Candellia wax, Carbowax, Carnbauba wax, Fisher-Tropsch waxes, Montan wax, Ozocerite, petroleum waxes, including paraffin wax, microcrystalline wax, and their mixtures. Preferably the waxy substance employed in the aqueous emulsion of the present invention is selected from the group consisting of paraffin wax, microcrystalline wax, crystalline or slack wax, and mixtures thereof.
Aqueous emulsions of a waxy substance utilized in the process and composition of the present invention can be prepared by heating the waxy substance to a temperature sufficient to cause the waxy substance to flow, for example by heating the waxy substance above its melting point, and mixing, for example by spinning at a relatively high speed, the waxy substance in its flowable condition with water, and preferably with a surfactant. Aqueous emulsions of wax emulsions are commercially available. One example of a commercially available aqueous emulsion of a microcrystalline wax, i.e., a paraffin emulsion, is marketed by Hercules Incorporated, Wilmington, Del., U.S.A. under the product name MICROLUBE(copyright) N Paraffin Wax Emulsion. Another commercially available aqueous emulsion which can be used in the composition and process of the present invention, which is also marketed by Hercules Incorporated, and which is also a paraffin wax emulsion is PARACOL(copyright) 802 N Paraffin Emulsion.
Typically these new emulsions are stabilized in an aqueous emulsion with a surfactant such as alkali metal salts of fatty acids, alkali metal salts of sulfated fatty acids, alkali metal alkyl sulfates, alkali metal alkyl sufonates, alkali metal aryl sufonates, alkali metal alkyl lauryl sulfonate, alkali metal salts of alkylated naphthalene, alkali metal salt of lignosulfonic acid, condensation products of ethylene oxide and polyalkylene glycols, fatty acid glycerides, fatty acid amides, polyethylene sorbitol esters of fatty acids, quarternary ammonium halides, sorbitan esters, sulfonated or sulfated fatty acid esters or amides, and sulfonic acid. For example, excellent results have been achieved with sodium lignosulfonate as the surfactant, particularly with slack wax as the waxy substance in the emulsion.
Unexpectedly, very little aqueous emulsion is required to achieve substantial improvement in the resistance of the cementitious product to water penetration while maintaining the strength of the product. It has been found that as little as about 0.25% by weight of waxy substance to the weight of total water used in the water, cement and aggregate mixture provides substantial improvement in the resistance of the product to water penetration, is while maintaining the strength of the product, while amounts above about 20% by weight of waxy substance to the weight of water in the mixture provide almost no further improvement in the resistance of the product to water penetration. Preferably the waxy substance in the emulsion constitutes from about 0.35% to about 10% of the water in the mixture noted above, and most preferably from about 0.5% to about 5% of the water in the mixture.
Further, unexpectedly, only a small amount of aqueous emulsion of waxy substance, i.e., of wax or rosin, is needed to substantially improve the early strength of cement aggregate products, particularly such cement aggregate products as block or other products prepared by pouring the cement, aggregate and aqueous ingredient into a mold. It has been found that amounts of the waxy substance as small as 0.25% by weight based on the weight of the cement ingredient in the mixture of cement, aggregate, and aqueous ingredient of water and aqueous emulsion of the waxy substance. Preferably for greater increase in early strength, at least approximately 0.50% by weight of waxy substance based on the weight of cement, and most preferably at least approximately 0.75 by weight of waxy substance based on the weight of cement.
Still further, unexpectedly, the addition of the aqueous emulsion of a waxy substance to the water, cement and aggregate mixture permitted a reduction in the amount of water required to form a workable mixture, i.e., the amount required for acceptable xe2x80x9cslumpxe2x80x9d, from the amount of water that would otherwise be required by equivalent weight substitution of emulsion for water. This surprising desirous effect advantageously permits greater flexibility in formulating compositions for producing cementitious products, and unexpectedly provides lighter weight products having strength equivalent to the heavier weight mixtures without the additional water.
Another unexpected advantage is that the waxy substance slows ah the evaporation of the excess water from the concrete as it cures. It commonly takes as long as two weeks for the majority of water to hydrate the cement. Often sheets of plastic or other materials are placed overly fresh poured concrete to slow the evaporation rate of the water internally to the mix. The resulting fully hydrated concrete is stronger than samples that have not been covered with plastic or the other material. It has now been found that the waxy substance in the emulsion in the present invention slows the rate At of evaporation of the free water, i.e., the water above the amount required to hydrate the cement. For example, in one case the control sample turned white within two days, whereas the sample with the waxy substance admix remained gray for about five days and the waxy substance emulsion containing sample retained its weight longer than the control sample indicating that the evaporation rate of the emulsion containing sample was desirably substantially reduced.
The composition and process of the present invention further provides an advantageous vehicle for introducing property enhancing agents into cementitious products in addition to improving the resistance of the products to the penetration and/or absorption of water into the products. These agents or additives may be dissolved in the waxy substance upon melting of the latter prior to the formation of the emulsion. If the agent is insoluble in the waxy substance, a co-solvent may be utilized to form a homogenous mixture, after which the latter can be made into the aqueous emulsion, and if desired, a surfactant incorporated. Such property enhancing agents can include mildew reducing agents, algae reducing agents, coloring agents, free radical scavengers, ultraviolet radiation absorption inhibiting agents, light stabilizing agents, corrosion inhibiting agents, and oxidation inhibiting agents, among others.
Among the property enhancing agents which can be successfully incorporated in property enhancing amounts in the compositions, and in accordance with the process of this invention, are: NUOCIDE(copyright)1071 Algicide, a non-metallic organic algicide marketed by Hxc3xcls America Inc., Somerset, N.J., USA, either alone or with NUOCIDE(copyright) 404D or NUOCIDE(copyright)0960, also marketed by Hxc3xcls America Inc. (NUOCIDE is a registered trademark of Hxc3xcls America Inc.), preferably in a ratio of 0.8% NUOCIDE 440D to 0.1-0.2% NUOCIDE 1071 by weight of the total composition; MERGALOS(copyright)S90 Algicide marketed by Allied Signal, Inc., Morristown, N.J., USA (MERGAL is a registered trademark of Allied Signal, Inc.); IRGAROL(copyright) 1071 Algicide marketed by Ciba Specialty Chemical Corporation, Tarrytown, N.Y., USA (IRGAROL is a registered trademark of Ciba Chemicals Corporation), and is also distributed by Allied Signal, Inc., Hxc3xcls America, Inc. and Troy Corporation, Florham Park, N.J. USA; TINUVIN(copyright)292, TINUVIN(copyright)144 and TINUVIN(copyright)123 hindered amine light stabilizers, TINUVIN(copyright)328, TINUVIN(copyright)384, TINUVINID(copyright)900, TINUVIN(copyright)928, and TINUVIN(copyright)1130 hydroxyphenylbenzotriazole ultraviolet light stabilizers, TINUVIN(copyright)400 hydroxyphenyltriazine ultraviolet radiation absorber, marketed by Ciba Specialty Chemicals Corporation (TINUVIN is a registered trademark of Ciba Specialty Chemicals Corporation). IRGANOX(copyright)1010 and IRGANOX(copyright)1076 phenolic antioxidants marketed by Ciba Specialty Chemicals Corporation, (IRGANOX is a registered trademark of Ciba Specialty Chemicals Corporation); IRGANOX(copyright)1035 antioxidant and peroxide antidecomposer marketed by Ciba Specialty Chemicals Corporation; IRGANOX(copyright)B Blends of antioxidants and phosphite peroxide antidecomposer marketed by Ciga Specialty Chemicals Corporation; IRGACOR(copyright)153 C12-14 tert-alkamines compounds with (2-benzothiazolylthio)-butanedocic acid (2:1) xylenes corrosion inhibitor, IRGACOR(copyright)0252 LD crystalline corrosion inhibitor and IRGACOR(copyright)225LD corrosion inhibitor, all marketed by Ciba Specialty Chemicals Corporation, (IRGACOR is a registered trademark of Ciba Specialty Chemicals Corporation); and sodium nitrite as a corrosion inhibitor.
Of particular advantage of the present invention is the resistance of cement aggregate products of the present invention to both the penetration and absorportion of water, and the improved resistance to the growth of mildew and mold on the surfaces of the products. These advantages are achieved through the incorporation of the aqueous emulsion of the waxy substance in the aqueous ingredient of the cement, aggregate and water mixture, and the use of a biocide, such as an algaecide or fungacide, as heretofore noted, either as a surface treatment or as an enhancing agent dissolved in the waxy substance aqueous emulsion.
As a typical composition in accordance with the present invention, the waxy substance in the aqueous emulsion thereof may constitute. approximately 50% of the emulsion, and the amount of emulsion employed calculated to be about 0.5%-20% of waxy substance,: for example wax, to the total amount of water in the water, cement and aggregate mixture. In the following example, except for the control which did not contain any aqueous emulsion of a waxy substance, the aqueous emulsion of waxy substance was MICROLUBE(copyright) C marketed by Hercules Incorporated, which contained 48% microcrystalline wax.